The invention relates to a tool for inserting prostheses within the body, and more particularly to tools for inserting prostheses, such as artificial discs and cages, within an intervertebral space.
Spinal surgery involves many challenges as the long-term health and mobility of the patient often depends on the surgeon""s technique and precision. One type of spinal surgery involves the removal of the natural disc tissue that is located between adjacent vertebral bodies. Procedures are known in which the natural, damaged disc tissue is replaced with an interbody cage or fusion device, or with a disc prosthesis.
The insertion of an article, such as an artificial disc prosthesis, presents the surgeon with several challenges. The adjacent vertebral bodies collapse upon each other once the natural disc tissue is removed. These bodies must be separated to an extent sufficient to enable the placement of the prosthesis. However, if the vertebral bodies are separated, or distracted, to beyond a certain degree, further injury can occur. The disc prosthesis must also be properly positioned between the adjacent vertebral bodies. Over-insertion, or under-insertion of the prosthesis can lead to pain, postural problems and/or limited mobility or freedom of movement.
Specialized tools have been developed to facilitate the placement of devices, such as disc prosthesis, between adjacent vertebral bodies of a patient""s spine. Among the known tools for performing such procedures are separate spinal distractors and insertion devices. The use of separate tools to distract the vertebral bodies and insert a disc prosthesis or graft can prove cumbersome. Further, the use of some distractors can cause over-distraction of the vertebral bodies.
Exemplary devices for installing prosthesis and/or grafts between vertebral bodies are disclosed in U.S. Pat. Nos. 5,431,658 and 5,505,732. U.S. Pat. No. 5,431,658 discloses a facilitator device for the insertion of bone grafts between two adjacent vertebrae. The disclosed tool has two flat, tong-like guides that distract the vertebrae as a screw-type inserter forces the graft between the distracted vertebrae. U.S. Pat. No. 5,505,732 discloses an apparatus and a method of inserting spinal implants. The intervertebral space is first distracted and a hollow sleeve having teeth at one end is then driven into the vertebrae that are adjacent the disc space. A drill is then passed through the hollow sleeve, removing the disc and the bone in preparation for receiving the spinal implant, which is then inserted through the sleeve.
Despite existing tools and technologies, there remains a need to provide a device to facilitate the proper and convenient insertion of an object, such as a disc prosthesis, between adjacent vertebral bodies while minimizing the risk of further injury to the patient.
The present invention provides a device useful for implanting prostheses, such as artificial spinal discs and cages, within a patient in a safe and efficient manner. The installation tool of the invention generally includes a pair of opposed levers, each of which has a proximal handle portion and a distal portion. A fulcrum is disposed between the two levers to enable proper operation of the tool. The tool further includes a pusher block that is positioned between the two levers and is selectively movable between an initial location distal of the fulcrum and a final location adjacent the distal end of the levers. The pusher block includes a proximal end, a distal end, and a bore extending at least partially therethrough. A pusher rod, which facilitates movement of a pusher block, has a distal end extending into the bore in the pusher block and a proximal, handle end.
The pusher rod and/or pusher block can be adapted to mate to a variety of prosthesis devices. In one embodiment, the pusher block can include a blind bore and a distal end of the pusher rod can mate with the blind bore in the pusher block. The pusher block can thus include a distally facing surface having surface features adapted to conform to or mate with complementary surface features on a prosthesis. In another embodiment, the bore can extend entirely through the pusher block to allow a distal end of the pusher rod to extend through the bore in the pusher block. The pusher rod can thus include a distal tip that is effective to mate to a prosthesis.
In yet another embodiment, the rod can include a first externally threaded distal portion and a second externally threaded distal portion. The second distal portion is positioned proximal to the first distal portion, and has a diameter greater than a diameter of the first distal portion. The bore of the pusher block can include a threaded proximal opening, a distal opening, and a chamber formed therebetween. The proximal opening is threadingly matable with the second distal portion of the rod to allow the second distal portion of the rod to be threadingly inserted through the proximal opening and positioned within the chamber. The diameter of the distal opening of the pusher block should be less than the diameter of the proximal opening of the pusher block to prevent the second threaded portion of the rod from extending through the distal opening in the pusher block. The threaded second distal portion is preferably freely rotatable within the chamber of the pusher block. The threaded first distal portion of the rod extends through the distal opening in the pusher block and includes a distal tip which is adapted to mate to a prosthesis.
In other aspects of the invention the bore extends entirely through the pusher block and a distal tip of the pusher rod is adapted to extend through the bore in the pusher block. The distal tip of the pusher rod is further adapted to mate to a grasping element effective to releasably engage a prosthesis. The grasping element can include an elongate proximal portion with a bore formed therein and a distal portion that is effective to releasably engage a prosthesis. The proximal portion has an outer diameter that is adapted to fit within the bore of the distal end of the pusher block. The distal portion of the grasping can include opposed first and second components that are movable between a first, open position, and a second, closed position that is effective to engage a prosthesis. In use, the distal end of the rod threadingly engages the bore of the grasping element. Rotation of the rod in a first direction is effective to cause the elongate proximal portion of the grasping element to move proximally within the bore of the pusher block, thereby moving the first and second components to the second, closed position. Rotation of the rod in a second, opposed direction is effective to cause the elongate proximal portion of the grasping element to move distally out of the bore of the pusher block and move the first and second components to the first, open position. The first and second components can optionally include at least one surface feature effective to engage a prosthesis.
In yet another embodiment, a medical device installation kit can be provided having a pair of opposed levers, a fulcrum disposed between the levers for allowing pivotal movement of the levers with respect to each other, and a plurality of prosthesis installation assemblies. Each assembly is adapted to be slidably disposed between the levers and movable between a first, proximal position and a second, distal portion. A handle portion can be provided on each assembly for moving the prosthesis installation assembly between the first and second positions. Each assembly further includes a distal prosthesis effecting element adapted to place a prosthesis between adjacent bone structures.
In one embodiment, one of the prosthesis installation assemblies includes a pusher block having a proximal end, a distal end, and a bore extending therethrough, a pusher rod slidably disposed between the levers and extending through the bore in the pusher block, and a grasping element effective to releasably engage a prosthesis. In another embodiment, one of the prosthesis installation assemblies includes a pusher rod having a proximal handle portion and a distal portion having a distal tip adapted to positively engage a prosthesis. A pusher block can be provided having a bore extending therethrough and adapted to receive a distal portion of the pusher rod. In yet another embodiment, one of the prosthesis installation assemblies can include a pusher rod having an externally threaded first distal portion and an externally threaded second distal portion. The second distal portion has a diameter greater than the first distal portion, and is positioned proximal to the first distal portion. The assembly further includes a pusher block having a bore extending entirely therethrough having a threaded proximal opening that is threadingly matable with the second distal portion of the rod, and a distal opening having a diameter less than the diameter of the second distal portion of the rod. A chamber having a diameter greater than the diameter of the second distal portion of the pusher rod is disposed between the first and second openings of the pusher block. In other aspects, one of the prosthesis installation assemblies can include a pusher block having a bore extending therethrough, a pusher rod extending through the bore in the pusher block, and a plurality of connector elements having a proximal portion adapted to mate to a distal tip of the pusher rod, and a distal portion adapted to mate to a prosthesis.
The installation tool of the invention can be used in the following manner. Once the natural, damaged disc tissue is removed from a patient and the area is prepared to receive an artificial prosthesis, such as an artificial disc, the artificial disc is loaded between the levers of the installation tool so that a posterior side of the disc abuts a distal end of the pusher block. The distal tip of the levers is then positioned between the vertebral bodies such that the outwardly facing surfaces of each lever contacts opposed vertebral bodies. Once this position is achieved, the pusher rod is advanced distally, causing the pusher block and the artificial disc to likewise move distally along the inner surfaces of the levers. As the artificial disc and the pusher rod move distally, or forward, the levers separate and also cause vertical separation of the adjacent vertebral bodies. To achieve the proper position of the artificial disc, the distal facing surfaces of the pusher block should contact the vertebral bodies. Once such contact is achieved between the distal facing surfaces of the pusher block and the vertebral bodies, the artificial disc is properly positioned. This tool thus enables the proper positioning of the artificial disc between the vertebral bodies, without over-insertion or under-insertion of the artificial disc, while minimizing the degree of distraction of the vertebrae. To remove the tool, a slaphammer or similar device can be used to apply a proximally directed force to the tool to extract the blade tips without removing the implant.